The data traffic amount grows along with the growing development of mobile Internet and multi-media applications. It is going to be an era of fourth generation (4G) communication. For the placement of 4G base stations, in addition to the consideration of the coverage areas of the large base stations, small equipment may be used to extend the coverage areas of the base stations in some areas where the signal quality is not good or in some areas which is not suitable for the placement of large base stations, such as tunnels or inside a building. One of the technologies to implement is radio over fiber (RoF), by which signals are transmitted over an optical fiber. The RoF technology could extend the coverage areas easily, be simple to implement, and be with low cost. Therefore, when the operators place base stations, 4G RoF solution may be used to enlarge the coverage areas and solve the problems such as environments where signal quality is poor or high data traffic.
There are two main systems, Worldwide Interoperability for Microwave Access (WiMAX) and Long Term Evolution (LTE), for 4G communication. In addition, the operators often provide Wi-Fi hotspots to support large data traffic in crowded places. Therefore, there is a need for 4G RoF systems to support multiple systems. Nowadays, the operators place one RoF equipment for each system, which increases the cost and space to place the equipment.